Logic, therefore, as the science of thought, or the science of the process of pure reason, should be capable of being constructed a priori.  Dialectic, for the most part, can be constructed only a posteriori; that is to say, we may learn its rules by an experiential knowledge of the disturbance which pure thought suffers through the difference of individuality manifested in the intercourse between two rational beings, and also by acquaintance with the means which disputants adopt in order to make good against one another their own individual thought, and to show that it is pure and objective.  For human nature is such that if A. and B. are engaged in thinking in common, and are communicating their opinions to one another on any subject, so long as it is not a mere fact of history, and A. perceives that B.’s thoughts on one and the same subject are not the same as his own, he does not begin by revising his own process of thinking, so as to discover any mistake which he may have made, but he assumes that the mistake has occurred in B.’s.  In other words, man is naturally obstinate; and this quality in him is attended with certain results, treated of in the branch of knowledge which I should like to call Dialectic, but which, in order to avoid misunderstanding, I shall call Controversial or Eristical Dialectic.  Accordingly, it is the branch of knowledge which treats of the obstinacy natural to man.  Eristic is only a harsher name for the same thing.

Controversial Dialectic is the art of disputing, and of disputing in such a way as to hold one’s own, whether one is in the right or the wrong—­per fas et nefas.[1] A man may be objectively in the right, and nevertheless in the eyes of bystanders, and sometimes in his own, he may come off worst.  For example, I may advance a proof of some assertion, and my adversary may refute the proof, and thus appear to have refuted the assertion, for which there may, nevertheless, be other proofs.  In this case, of course, my adversary and I change places:  he comes off best, although, as a matter of fact, he is in the wrong.

[Footnote 1:  According to Diogenes Laertius, v., 28, Aristotle put Rhetoric and Dialectic together, as aiming at persuasion, [Greek:  to pithanon]; and Analytic and Philosophy as aiming at truth.  Aristotle does, indeed, distinguish between (1) Logic, or Analytic, as the theory or method of arriving at true or apodeictic conclusions; and (2) Dialectic as the method of arriving at conclusions that are accepted or pass current as true, [Greek:  endoxa] probabilia; conclusions in regard to which it is not taken for granted that they are false, and also not taken for granted that they are true in themselves, since that is not the point.  What is this but the art of being in the right, whether one has any reason for being so or not, in other words, the art of attaining the appearance of truth, regardless of its substance?  That is, then, as I put it above.